The present invention relates to optical information conversion processing and in particular, relates to an improved spatial-light modulator suitable for display and the analog parallel processing of moving and still pictures.
In recent years, there have been expectations for a spatial-light modulator that operates at a high speed and that has a fast response, as a device for the processing and display of optical information such as images and the like.
A conventional spatial-light modulator is shown in FIG. 1A and 1B, for example. The description of this conventional spatial-light modulator will start with reference to FIG. 1A. This spatial-light modulator was presented at the Autumn, 1989 meeting of the Applied Physics Society. In the figure, a dielectric mirror 12 is sandwiched between a photoconductive unit 14 by BSO and a polymer dispersed liquid crystal unit 10 comprising a polymer and a nematic liquid crystal. Then, these are sandwiched between transparent electrodes 16 and 18 by ITO and to the side of the transparent electrode 18 is laminated a glass substrate 20. Between the transparent electrodes 16 and 18 is connected a power supply 22 for drive.
When there is information write, the write light P1 such as that from an argon (Ar) laser or the like, is irradiated with respect to the photoconductive unit 14 as shown by the arrow in the diagram (the direction to the right, on the left side), and the optical information that is included in the laser light is stored as electrical charges. On the other hand, the read light P.sub.2 such as that of a helium-neon (He-Ne) laser or the like is irradiated to the liquid crystal compound unit 10 as shown by the arrow (direction to the left). This liquid crystal compound unit 10 is influenced by the electric field due to the electrical charge of the photoconductive unit 14. Because of this, the read light P.sub.2 receives considerable modulation due to the electrical charge. This read light P.sub.2 is reflected by the dielectric mirror 12 and is output as the output light P.sub.3 as shown by the arrow (right direction on the right side).
FIG. 1B shows a spatial-light modulator that was disclosed in the text of J. Phys. D: Appl. Phys. 21 (1988) S156-159/ECOOSA'88 of GEC Research Ltd. & STC Technology Ltd. In the figure, hydrogenated amorphous silicon (hereinafter termed "a-Si:H") is used to laminate a photoconductive unit 26 to the optical modulator unit 24 that comprises a smectic liquid crystal and they are sandwiched by a transparent electrodes 28 and 30 of indium-tin oxide. To the outer sides of the transparent electrodes 28 and 30 are laminated glass substrates 32 and 34. Then, a power source 36 for drive is connected across the transparent electrodes 28 and 30. The procedures for information write and read are the same as for the conventional example shown in FIG. 1A.
Another example of a conventional spatial-light modulator is a ferroelectric liquid crystal spatial-light modulator that is shown in FIG. 2A, and this is disclosed in a paper "27a-ZF-2" of the Applied Physics Society Technology Presentations of Autumn, 1989, as "Optical Pattern Recognition with LAPS-SLM (1): Optical-write type of ferroelectric liquid crystal light valve".
As shown in the same figure, this ferroelectric liquid crystal spatial-light modulator 1 has in sequence from the right side of the figure which is the side that irradiates the write light P1, a glass layer 2, an ITO electrode layer 3, a hydrogenated amorphous silicon (a-Si:H) single-layer photoconductive unit 4, an alignment film layer 5, a liquid crystal layer 6, an alignment film layer 5, an ITO electrode layer 3 and a glass layer 2, and between these alignmentd film layers 5, 5 is a spatial-light modulator with a laminated structure inserted between the spacers 7, 7. Here, there is a hydrogenated amorphous silicon (a-Si:H) single-layer photoconductive unit 4 and a liquid crystal layer 6 between the ITO electrode layers 3, 3.
In addition, another reflection type of spatial-light modulator shown in FIG. 2B, is disclosed in "28p-ZD-6" of the Applied Physics Society Technology Presentations of Autumn, 1989, as "Reflection made spatial-light modulator using a polymer-dispersed liquid crystal and BSO crystal (I)".
As shown in the same figure, this reflective type spatial-light modulator 8 has in sequence from the left side of the figure which is the side from which the write light P.sub.1 is irradiated, a photoconductive crystal layer 14 of Bi.sub.12 SiO.sub.20 (BSO), a transparent electrode 9 of ITO, a dielectric multi-layer mirror layer 12, a liquid crystal compound layer 10 comprising a polymer and a nematic liquid crystal, an ITO electrode layer 9 and a glass substrate 13 which are laminated to form the spatial-light modulator.
However, there are the following problems in such conventional technology as has been described above.
(1) In the conventional technology shown in FIG. 1A, BSO is used as the photoconductive crystal layer 14 and so it is necessary to have high-precision grinding in the process for the manufacture of the element. In addition, BSO is a crystal material and so it is difficult to have large surface areas and the manufacturing cost is also high. In addition, when the read light is strong, this read light reaches the photoconductive crystal layer 14 after passing the dielectric mirror 12 and the charge image is dispersed to deteriorate the resolution and the contrast ratio of the read image.
(2) Next, in the conventional example shown in FIG. 1B, a-Si is used as the photo-conductive unit 26 and so it is easily manufactured with large areas. However, when a strong write light is irradiated to the photoconductive unit 26, the hydrogen (H) is separated and the configuration changes to cause deterioration of the photo-conductive unit 26 and cause "burning" of the image.
(3) The BSO photoconductive crystal layer 14 of the reflective type spatial-light modulator 8 and the hydrogenated amorphous silicon (a-Si:H) single-layer photoconductive unit 4 of the conventional spatial-light modulator 1 both have a small xerographic sensitivity (hereinafter referred to as the sensitivity) in the long wavelength region of the write light P.sub.1 (incident light) and so the intensity of the write light P.sub.1 must be made strong but when the intensity of the write light P.sub.1 is intensified, there is the problem of this causing a lowering of the contrast ratio in the read image obtained.
(4) Here, although it is not indicated in the diagram, there is a laminated structure the same as that of the conventional ferroelectric liquid crystal spatial-light modulator 1 and the reflective type spatial-light modulator 8 shown in FIG. 2A and FIG. 2B, and when the hydrogenated amorphous silicon (a-Si:H) single-layer photoconductive unit 4 and the photoconductive crystal layer 14 are used in photoconductive layers having different configurations (such as a photoconductive layer comprised of laminations of a hydrogenated amorphous silicon layer and another photoconductive layer), a boundary surface is created between the two layers and the response speed of the spatial-light modulator drops as a result of the drop in mobility of the charge that occurs inside the photoconductive layer in accordance with the write light P.sub.1 and this causes the problem that it is not possible to continuously and clearly process images of objects moving rapidly.